Vacuum insulation structures for high-temperature batteries have created efficient insulation assemblies effecting heat transfer by radiation, conduction through the solid structure, and conduction through residual gases within the loose multi-foil insulation. Such multi-foil insulation may consist of thin metal foil separated by glass or other thermal insulator material. Attempts have been made to strengthen the casing walls of the loosely wrapped multi-foil insulation and to form a satisfactory load bearing insulation by compressing multi-foil sheet structures at elevated temperatures. Those attempts have resulted in partial sintering of the glass paper where such is used to separate aluminum foil sheets. As a result, while the thermal jacket strength is adequate, the thermal conductivity thereof is significantly increased.
U.S. Pat. No. 5,347,816 entitled "VARIABLE PRESSURE THERMAL INSULATING JACKET" and issued Sept. 20, 1994 to Paul A. Nelson et al. is representative of developments within this art. In the various devices forming embodiments of the invention, a thermal jacket having a closed volume capable of being evacuated to form an insulating jacket and incorporating a loosely wrapped insulation layer is interposed between an outside jacket casing and one or more bipolar batteries. In one form, multi-foil insulation layers are created by wrapping sectional widths of the multi-foils separated by glass paper in edge overlapping, side-by-side fashion to double the density of the multi-foil material at the overlapping ends of the wrapped sections, thereby assisting in maintaining the position of the centrally located battery or batteries without compression of the main body of insulation.
While improving the ability of the loose multi-layer structure to support the inner cylinder, the density increase of the edge overlapped foil content layers tends to create high thermal conductivity areas at the spaced longitudinal positions defined by the edge overlapping multi-foils.
It is therefore an object of this invention to create a high efficiency thermal insulation structure with a load bearing system which does not materially detract from the thermal insulation of the assembly provided by the loose multi-foil material and to eliminate the thermal short circuit and leak problems at the interface between the sectional multi-foil structures of the prior art as exemplified by the prior art above.
It is a further object of the invention to provide a permanent getter within such structure which absorbs all kinds of gases but hydrogen, and which functions as a reversible getter when heated to release hydrogen once the enclosure has been made thermally conductive while reabsorbing hydrogen during cooling when the enclosure is required to perform in the insulation mode.
It is a further object of the present invention to provide such high efficiency thermal insulation structure with an effective, integrated load bearing system utilizing loose multi-foil layers in which the foil content is perforated to ensure radial gas diffusion and which facilitates degassing without adversely affecting the thermal insulation performance of the structure.